More than a third of adults ages 55 and older report sleeping less than 7h per night on a regular basis,[unreadable] with nearly 15% sleeping <6h per night. The consequences of acute sleep deprivation are well understood,[unreadable] but far less is known about the effects chronic insufficient sleep, particularly in older people. Evidence[unreadable] gathered during the previous grant periods strongly suggests that the sleep quality of older people is[unreadable] extremely vulnerable to a misalignment between the timing of sleep and the phase of the circadian timing[unreadable] system suggests that older people will be less able than young adults to obtain needed recovery sleep[unreadable] following acute sleep loss. There is also compelling evidence that the interaction between the two major[unreadable] sleep regulatory processes, the circadian and the sleep-wake homeostat, changes with age. We propose a[unreadable] study that will assess the effects of chronic sleep restriction in young and older adults, using a study design[unreadable] that will allow us to quantify age-related differences in the impact of circadian and sleep-dependent[unreadable] influences on sleep.[unreadable] The proposed investigation is designed to test the following hypotheses: 1) that notwithstanding the[unreadable] increased homeostatic sleep pressure induced by chronic sleep restriction, sleep will be significantly more[unreadable] disrupted when it is scheduled at adverse circadian phases in older as compared with young adults; 2) that[unreadable] under conditions of chronic sleep restriction, slow-wave activity during sleep will be increased at all circadian[unreadable] phases in both young and older subjects; 3) that the circadian rhythm of REM sleep will be preserved across[unreadable] 4 weeks of chronic sleep restriction in young and older subjects, and that it will be preserved in older[unreadable] subjects at the expense of other sleep stages, including slow-wave sleep; and 4) that unlike the sleep of[unreadable] young subjects, during sleep extension following 4 weeks of chronic sleep restriction, the sleep of older[unreadable] subjects will not show rapid recovery as measured by the duration and intensity of slow-wave sleep, sleep[unreadable] efficiency, and number of awakenings.[unreadable] We propose to test these hypotheses in healthy young and older men and women whose sleep-wake[unreadable] cycle is scheduled to a 28-h day under conditions of chronic sleep restriction (i.e., 22.17 h wake followed by[unreadable] 5.83 h sleep opportunity) on a forced desynchrony protocol across 4 weeks. Polysomnographic sleep[unreadable] recording and quantitative analysis of EEC will be used to describe age-related changes in circadian sleep[unreadable] regulation and to understand the effects of chronic sleep restriction on sleep in older persons.[unreadable] The results of this project will provide important information on the effects of chronic insufficient sleep in[unreadable] older people, a condition which a significant portion of the older population experiences on a regular basis,[unreadable] and an area of investigation in which few laboratory-based investigations have been conducted.[unreadable]